How to fix the pressure of a Junkers Cerastar ZWR 18-5 KE 23 gas furnace?

Hello,

I don't know if this is the right place to ask, but maybe there is someone with the skills.

We have a gas furnace at home, for the central heating of the house and for the hot water of the taps.
The model of this furnace is Junkers Cerastar ZWR 18-5 KE 23 from Bosch.
I live in Germany and the instruction manual is in German only.

The problem:
The heater works perfectly and there is hot water and heating in all the rooms,
but the pressure of the pipeline for the house heating is under the recommended 1 Bar.
See the attached picture.



How to fix it:
In the manual it says: "If the pressure is too low, you need to open a valve, to let water in to the pipelines, while keeping an eye on the pressure gauge until it reads again 1 Bar. Then you close the valve." But I cannot find the said valve.

The question:
Do you know how to refill this one?
Where is the valve that I should turn on?

Not really the right place to ask but I have a similar setup in a heating system so I might be able to help.

The guage tells you the water pressure in the heating loop - the pipe that passes the hot water from one radiator to the next then back to the furnace. The valve it refers to is the one that feeds water to the system from your house cold water supply, I can't tell which that is from the pictures I'm afraid.

The house water supply is at > 1 bar pressure (mine is unusually high at 6 bar but 2 - 3 bar is more usual) so opening the valve lets water from your high pressure domestic supply flow into the lower pressure heating system. There should be a non-return (one way) valve in the line as well to prevent the water flowing back if the pressures are reversed. You need to find the cold feed pipe from your house incoming water supply and the valve will be the one connecting it to the furnace. Open the valve slowly and the guage should start to rise, be ready to close the valve as soon as 1 bar pressure is reached. It is only used to pressurize a new system and to 'top-up' the pressure due to leakage and venting of the radiators, it should normally be left closed.

If I had to guess, it is the one marked 173 on the diagram.

Brian.

We had a house with a similar system (it burned oil). It had several valves.

I agree, 173 (Kaltwasser). A competent installer should give you a handle that admits water to the system. Is that a yellow handle sitting near the top? I'll bet it fits 173. Feel whether the pipe gets cold as you open it.

Surprising if the heater is still working with zero water pressure. There should be a low pressure limit switch stopping it.

I would be cautious with simply refilling. Either there's a massive leak, or the manometer is defective.

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According to manual, ZWR 18 has a low pressure switch tripping below 0.5 bar.